Reference library
What is in my water?
16 contaminants that occur in Indian drinking water, each with the published BIS and WHO limits, where it comes from, whether you could ever detect it yourself, which technology removes it — and, just as importantly, which widely-sold technology does nothing at all.
Most Indian water purifier purchases are made on a single number — the reading on a handheld TDS meter, usually held by someone selling a purifier. That number tells you how easily electricity crosses your water. It does not tell you what is in it.
This library exists to make the other question answerable. Each entry covers one contaminant and answers the same five things in the same order: what the limits are and who set them, where it comes from, whether you could possibly detect it without a laboratory, what removes it, and what does not remove it despite being sold as if it did.
The last of those is the part you will not find on a manufacturer's site, and it is where the money is lost. A household that installs RO for a bacteriological problem, or a UV unit for fluoride, or a softener for salty water has bought equipment that cannot address what they bought it for — and will conclude, reasonably, that water treatment does not work.
Physical parameters
2 entries
- Total Dissolved Solids (TDS)Total Dissolved Solids is the combined mass of everything dissolved in water — minerals, salts and metals — expressed in milligrams per litre (mg/L), which handheld meters display as ppm.500 mg/L · BIS IS 10500:2012
- TurbidityTurbidity is the cloudiness caused by suspended particles, measured in nephelometric turbidity units (NTU), and it is the parameter that determines whether UV disinfection can work at all.1 NTU · BIS IS 10500:2012
Metals & metalloids
4 entries
- ArsenicAsArsenic is a naturally occurring metalloid that dissolves out of aquifer sediments into groundwater, where it is colourless, tasteless and odourless at every concentration relevant to health.0.01 mg/L · BIS IS 10500:2012
- LeadPbLead is a heavy metal that enters drinking water almost entirely from plumbing — pipes, solder, brass fittings and taps — rather than from the source water itself.0.01 mg/L · BIS IS 10500:2012
- IronFeIron is a metal that dissolves into groundwater in its ferrous (Fe²⁺) form, invisible until it meets air and oxidises to ferric (Fe³⁺), which is the orange-brown particulate that stains everything it touches.0.3 mg/L · BIS IS 10500:2012
- UraniumUUranium is a naturally occurring radioactive metal that dissolves into groundwater from uranium-bearing rock, and whose drinking-water limit is set by chemical kidney toxicity rather than by radioactivity.0.03 mg/L · BIS IS 10500:2012 (as amended)
Inorganic ions & minerals
6 entries
- FluorideF⁻Fluoride is a naturally occurring ion released into groundwater by fluoride-bearing rocks, notable for having an unusually narrow band between beneficial and harmful concentrations.1.0 mg/L · BIS IS 10500:2012
- NitrateNO₃⁻Nitrate is the oxidised form of nitrogen, entering groundwater principally from fertiliser leaching and sewage, and it is the most widespread agricultural contaminant in Indian groundwater.45 mg/L (as NO₃) · BIS IS 10500:2012
- Total HardnessTotal hardness is the combined concentration of dissolved calcium and magnesium, expressed as milligrams per litre of equivalent calcium carbonate, and it is what forms scale on every surface hot water touches.200 mg/L as CaCO₃ · BIS IS 10500:2012
- Chloride & SalinityCl⁻Chloride is the ion responsible for the salty taste in water, entering groundwater from natural salt deposits, seawater intrusion in coastal aquifers, and sewage.250 mg/L · BIS IS 10500:2012
- CalciumCa²⁺Calcium is a dissolved mineral that, with magnesium, makes up total hardness, and is the principal component of the white scale that forms on heating elements and taps.75 mg/L · BIS IS 10500:2012
- MagnesiumMg²⁺Magnesium is the second component of water hardness after calcium, and the mineral most often responsible for a distinctly bitter taste in high-TDS groundwater.30 mg/L · BIS IS 10500:2012
Disinfectants & by-products
1 entry
Microbiological
2 entries
- Bacteria (E. coli & coliforms)Coliform bacteria and E. coli are indicator organisms — not usually dangerous themselves, but reliable evidence that water has been in contact with faecal material and may carry organisms that are.Shall not be detectable in any 100 mL sample · BIS IS 10500:2012
- VirusesWaterborne enteric viruses — rotavirus, norovirus, hepatitis A and E among them — are 10 to 100 times smaller than bacteria, which is why filtration that reliably stops bacteria does not reliably stop viruses.No separate viral parameter · BIS IS 10500:2012
Emerging contaminants
1 entry
The minimum water test worth paying for
If you do one thing after reading this library, get a panel done. A useful baseline for Indian supply, and what each parameter is there to catch:
- TDS, hardness, pH, chloride — establishes the character of your water and whether RO or softening is the right direction at all.
- Nitrate — the agricultural contaminant, essential if there is a bottle-fed infant in the house.
- Fluoride — decides whether you need defluoridation or already have a healthy level you should not remove.
- Iron — the single most useful pre-installation test on borewell water, because getting it wrong destroys RO membranes.
- Total coliform and E. coli — the microbiological check, and the one that can change within a day.
- Arsenic — add it if you are on groundwater in the Ganga–Brahmaputra belt. Not in a standard panel.
- Uranium — add it in Punjab, Haryana, Rajasthan, Andhra Pradesh or Telangana. Also not in a standard panel.
That is typically ₹1,200 to ₹3,000, against a purifier purchase of ₹10,000 to ₹25,000 and years of consumables. It is the cheapest decision in the whole process and the only one that tells you what you are buying for.
Frequently asked questions
Which water test should I get done in India?
Can a TDS meter tell me if my water is safe?
What is the difference between the BIS acceptable limit and the permissible limit?
Does RO remove everything from water?
How often should I test my water?
Sources
Every limit and standard quoted on this page comes from one of the documents below. Where a figure is not in one of these, we have not published it.
Bureau of Indian Standards · published 2012-05-01 · checked 2026-08-01
BIS states two figures for many parameters: an 'acceptable limit' and a 'permissible limit in the absence of an alternate source'. The second is a fallback for communities with no other supply, not a target.
Guidelines for Drinking-water Quality, 4th edition incorporating the 1st addendum
World Health Organization · published 2017-04-01 · checked 2026-08-01
Ground Water Quality in Shallow Aquifers — annual and state reports
Central Ground Water Board, Ministry of Jal Shakti, Government of India · checked 2026-08-01
District-level groundwater quality reporting. Coverage and sampling year vary by state — always check the report date for your district rather than assuming a national figure applies.
Limits quoted throughout this library are the published figures from the standards named on each page. They describe what the standard requires; they do not describe your supply. Only a laboratory result does that, and every entry names the test to ask for.